There are a lot of variables with just this one change. Posi? Tire diameter? Camshaft/redline? A 4.10 could make you spin off the line where a 2.73 might not. Also, if the cam is stock, you might run out of rpm's even in the 1/8th. Generally, 9 flat is approx. 14 flat in the 1/4. I wouldn't expect more than .5 sec at best assuming traction and everything else stayed constant.